Process gas abatement

ABSTRACT

A process gas abatement apparatus and method are disclosed. The process gas abatement apparatus comprises: a burner comprising: a combustion chamber operable to receive an effluent gas stream from a manufacturing process tool to be treated within the combustion chamber at a sub-atmospheric pressure, the combustion chamber being further operable to receive a fuel, oxidant and diluent, the fuel, oxidant and diluent controlling combustion within the combustion chamber to treat the effluent gas stream to produce a treated exhaust stream, the diluent being condensable in the treated exhaust stream. By providing a diluent in the form of, for example, an inert condensable, the volume gain within the combustion chamber is reduced, which reduces the volume of the exhaust stream and reduces the volumetric load on the second pump. The volume gain reduces because the diluent shifts phase in the exhaust stream, thereby effectively removing the contribution of the diluent to the volume of the exhaust stream. This leads to considerable power saving since a lower volume of gas is output from the combustion chamber which would need to be brought up to the second pressure, for example atmospheric pressure, by means of the second pump.

FIELD OF THE INVENTION

The present invention relates to a process gas abatement apparatus andmethod.

BACKGROUND OF THE INVENTION

Apparatus for treating an effluent gas stream from a manufacturingprocess tool operating at a sub-atmospheric pressure used in, forexample, the semiconductor or flat panel display manufacturing industryare known. During such manufacturing, residual perfluorinated compounds(PFCs) and other compounds exist in the effluent gas stream pumped fromthe process tool. PFCs are difficult to abate or remove from theeffluent gas and their release into the environment is undesirablebecause they are known to have relatively high greenhouse activity.

One way of performing effluent gas abatement is to pump the effluent gasfrom the process tool to a higher sub-atmospheric pressure before beingfed to a radiant burner. The radiant burner uses combustion to removethe PFCs and other compounds from the process gas stream. Typically, theeffluent gas stream is a nitrogen stream containing PFCs and othercompounds. A fuel gas is mixed with the effluent gas stream and that gasstream mixture is conveyed into a combustion chamber that is laterallysurrounded by the exit surface of a foraminous gas burner. Fuel gas andair are simultaneously supplied to the foraminous burner to affectflameless combustion at the exit surface, with the amount of air passingthrough the foraminous burner being sufficient to consume not only thefuel gas supplied to the burner, but also ail the combustibles in thegas stream mixture injected into the combustion chamber. The resultanttreated gas stream is exhausted from the radiant burner. Thereafter, thetreated gas stream is pumped to atmospheric pressure before beingvented.

Although techniques exist for processing the effluent gas stream, theyeach have their own shortcomings. Accordingly, it is desired to providean improved technique for processing an effluent gas stream.

SUMMARY

According to a first aspect, there is provided a process gas abatementapparatus, comprising: a burner comprising: a combustion chamberoperable to receive an effluent gas stream from a manufacturing processtool to be treated within the combustion chamber at a sub-atmosphericpressure, the combustion chamber being further operable to receive afuel, oxidant and diluent, the fuel, oxidant and diluent controllingcombustion within the combustion chamber to treat the effluent gasstream to produce a treated exhaust stream, the diluent beingcondensable in the treated exhaust stream.

The first aspect recognises that with existing approaches, as mentionedabove, the burner will be operated at a pressure between that of theprocess tool, but below atmospheric pressure. For example, the burner istypically operated at approximately 200 mbar, with process gases beingbrought up to this pressure by means of a multi-stage dry pumpingmechanism, with the combustion by-products being brought up to a secondpressure, for example atmospheric pressure by means of second pump suchas, for example, a liquid ring pump.

Typically, a hydrocarbon fuel provides the energy source for thecombustive abatement within the combustion chamber and often this fuelis methane. This burns with the process gas ‘P’ to produce a treatedprocess gas P′ according to reaction (1) below:

10P+CH₄+2O₂=CO₂+2H₂O+10P′  (1)

If it is assumed that atmospheric pressure combustion properties alsooccur for sub-atmospheric combustion, then each standard litre perminute (slm) of methane can abate around 10 standard litres per minuteof process exhaust. So with CH₄ and pure oxygen, the volumetric gainbetween the volume of gas being input to the combustion chamber and thevolume of gas being output by the combustion chamber is only 10% (i.e.10 slm of process exhaust is input into the combustion chamber and 11slm is output from the combustion chamber).

However, ordinarily, the O₂ would be delivered as 20.9% by volume in airand hence would be accompanied by a substantial volume of N₂. Using airis both a convenient source of O₂ and also is helpful within thecombustion chamber as the N₂ helps to moderate the flame speed andtemperature within the combustion chamber.

With air, burning as equation (2) below:

10P+CH₄+2O₂+8N₂=CO₂+8N₂+2H₂O+10P′  (2)

However, the first aspect recognises that the volumetric gain betweenthe volume of gas being input to the combustion chamber and the volumeof gas being output by the combustion chamber almost doubles (i.e. 10slm of process gas input into the combustion chamber and 19 slm outputfrom the combustion chamber).

Accordingly a process gas abatement apparatus may be provided. Theapparatus may comprise a burner. The burner may comprise a combustionchamber which receives a process or effluent gas stream from amanufacturing process tool. The effluent gas stream may be treatedwithin the combustion chamber at a sub-atmospheric pressure. Thecombustion chamber may receive a fuel, oxidant and diluent. The fuel,oxidant and diluent may control combustion within the combustion chamberto treat the effluent gas stream and produce a treated exhaust stream.The diluent may be condensable in the treated exhaust stream.

The first aspect recognises that since the purpose of the N₂ provided inexisting approaches is to moderate the flame speed and temperaturewithin the combustion chamber, it is only by convenience that N₂ is usedas it is ordinarily present in air. If this N₂ could be replaced with adiluent in the form of, for example, an inert condensable, the volumegain within the combustion chamber will be reduced, which reduces thevolume of the exhaust stream and reduces the volumetric load on thesecond pump. The volume gain reduces because the diluent shifts phase inthe exhaust stream, thereby effectively removing the contribution of thediluent to the volume of the exhaust stream. This leads to considerablepower saving since a lower volume of gas is output from the combustionchamber which would need to be brought up to the second pressure, forexample atmospheric pressure, by means of the second pump.

In one embodiment, the diluent, when introduced to the combustionchamber, comprises a vapour. Accordingly, the diluent may be mixed invapour form with the fuel and oxidant to effect combustion with therequired characteristics in order to treat the effluent gas stream. Thetransition from, for example, an inert condensable vapour to a liquidwithin the exhaust stream enables the diluent to both contribute to thecharacteristics of the combustion whilst also reducing the volume gainbecause the diluent shifts phase in the exhaust stream, therebyeffectively removing the contribution of the diluent to the volume ofthe exhaust stream.

In one embodiment, the diluent comprises a liquid prior to beingvaporised for introduction to the combustion chamber. It will beappreciated that this significantly simplifies storage of the diluent.

In one embodiment, the diluent condenses to a liquid in the treatedexhaust stream. It will be appreciated that the phase from a vapour to aliquid causes a significant reduction in volume.

In one embodiment, the diluent is introduced into the combustion chamberwith a first volumetric rate and occupies the treated exhaust streamwith a second volumetric rate, the second volumetric rate being lowerthan the first volumetric rate.

In one embodiment, the diluent is provided at specified volumetric rateto control combustion conditions within the combustion chamber to treatthe effluent gas stream.

In one embodiment, the diluent is combined with at least one of the fueland oxidant prior to being introduced into the combustion chamber. Itwill be appreciated that this significantly simplifies storage of thediluent and/or the fuel and oxidant.

In one embodiment, at least one of the fuel and the oxidant is dissolvedby the diluent prior to being introduced into the combustion chamber.

In one embodiment, both the fuel and the oxidant are dissolved by thediluent prior to being introduced into the combustion chamber.

In one embodiment, at least one of the fuel and the oxidant dissolved bythe diluent is vaporised prior to being introduced into the combustionchamber.

In one embodiment, at least one of the fuel and the oxidant dissolved bythe diluent and the diluent are co-vaporised prior to being introducedinto the combustion chamber.

In one embodiment, the diluent comprises at least one of water, aperfluorocarbon and a hydrocarbon.

In one embodiment, the burner comprises a radiant burner and thecombustion chamber has a porous sleeve through which the fuel, oxidantand diluent pass for combustion proximate to a combustion surface of theporous sleeve.

In one embodiment, the treated exhaust stream is provided to a liquidring pump for compression to atmospheric pressure.

In one embodiment, the diluent condenses in the liquid ring pump. Hence,the liquid ring pump may also act as an efficient condenser.

In one embodiment, the liquid ring pump is operable to scrub the treatedexhaust stream. Hence, the liquid ring pump may also act as an efficientscrubber.

According to a second aspect, there is provided a process gas abatementmethod, comprising: receiving an effluent gas stream to be treated froma manufacturing process tool within a combustion chamber at asub-atmospheric pressure, receiving a fuel, oxidant and diluent withinthe combustion chamber, the fuel, oxidant and diluent controllingcombustion within the combustion chamber to treat the effluent gasstream to produce a treated exhaust stream; and condensing the diluentin the treated exhaust stream.

In one embodiment, the step of receiving comprises introducing thediluent to the combustion chamber as a vapour.

In one embodiment, the diluent comprises a liquid prior to beingvaporised for introduction to the combustion chamber.

In one embodiment, step of condensing comprises condensing the diluentto a liquid in the treated exhaust stream.

In one embodiment, the step of receiving comprises introducing thediluent into the combustion chamber with a first volumetric rate and thestep of condensing comprises occupying the treated exhaust stream with asecond volumetric rate, the second volumetric rate being lower than thefirst volumetric rate.

In one embodiment, the step of receiving comprises providing the diluentat specified volumetric rate to control combustion conditions within thecombustion chamber to treat the effluent gas stream.

In one embodiment, the method comprises the step of combining thediluent with at least one of the fuel and oxidant prior to beingintroduced into the combustion chamber.

In one embodiment, the method comprises the step of dissolving at leastone of the fuel and the oxidant by the diluent prior to being introducedinto the combustion.

In one embodiment, the method comprises the step of dissolving both thefuel and the oxidant by the diluent prior to being introduced into thecombustion.

In one embodiment, the step of receiving comprises vaporising at leastone of the fuel and the oxidant dissolved by the diluent prior to beingintroduced into the combustion chamber.

In one embodiment, the step of receiving comprises co-vaporising atleast one of the fuel and the oxidant dissolved by the diluent and thediluent prior to being introduced into the combusion chamber.

In one embodiment, the diluent comprises at least one of water, aperfluorocarbon and a hydrocarbon.

In one embodiment, the burner comprises a radiant burner and thecombustion chamber has a porous sleeve through which the fuel, oxidantand diluent pass for combustion proximate to a combustion surface of theporous sleeve.

In one embodiment, the method comprises providing the treated exhauststream to a liquid ring pump for compression to atmospheric pressure.

In one embodiment, the step of condensing comprises condensing thediluent in the liquid ring pump.

In one embodiment, the method comprises the step of scrubbing thetreated exhaust stream using the liquid ring pump.

Further particular and preferred aspects are set out in the accompanyingindependent and dependent claims. Features of the dependent claims maybe combined with features of the independent claims as appropriate, andin combinations other than those explicity set out in the claims.

Where an apparatus feature is described as being operable to provide afunction, it will be appreciated that this includes an apparatus featurewhich provides that function or which is adapted or configured toprovide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, withreference to the accompanying drawings, in which:

FIG. 1 illustrates a process gas abatement apparatus according to oneembodiment.

DESCRIPTION OF THE EMBODIMENTS Overview

Before discussing the embodiments in any more detail, first an overviewwill be provided. In embodiments, a sub-atmospheric combustion system isoperated with a diluent which condenses in its exhaust stream in orderto reduce the volume of exhaust emitted. This reduces the volume ofexhaust which needs to be compressed to atmospheric pressure prior to bevented to atmosphere.

Process Gas Abatement

FIG. 1 illustrates a process gas abatement apparatus, generally 100,according to one embodiment. A first pump stage 10 evacuates a processchamber, such as a semiconductor process chamber, and takes a process oreffluent gas stream P provided at a first pressure, such as 1 mbar andcompresses the effluent gas stream P to an intermediate pressure, suchas 100-200 mbar. The first pump stage 10 typically comprises a dry pump.

A radiant burner 20 or other combustion apparatus receives the effluentgas stream P at the intermediate pressure. In addition, the radiantburner 20 receives a fuel/oxidant mixture, in addition to a diluent D.The effluent gas stream P is provided into a combustion chamber that islaterally surrounded by the exit surface of a foraminous gas burner. Thefuel/oxidant mixture is simultaneously supplied with the diluent D tothe foraminous burner to affect flameless combustion at the exitsurface. The amount of oxidant passing through the foraminous burner issufficient to consume not only the fuel supplied to the burner, but alsoall the combustibles in the effluent gas stream injected into thecombustion chamber. The diluent D is provided with an amount sufficientto control the flame speed at the exit surface of the foraminous burnerand to control the temperature and other combustion characteristicswithin the combustion chamber. The treated effluent gas stream P′ isexhausted from the radiant burner, together with the other by-productsof the combustion within the combustion chamber. The diluent D condenseswithin the treated effluent gas stream.

The treated effluent gas stream P′ is provided to a secondary pump stage30, such as a liquid ring pump, which compresses the treated effluentgas stream P′, together with the other by-products of the combustionwithin the combustion chamber to a second pressure, such as atmosphericpressure, prior to being vented to atmosphere.

EXAMPLE OPERATION

In this example, the effluent gas stream P is provided at a rate of 10slm (standard litres per minute) from the first pump stage 10 to theradiant burner 20. In order to treat the effluent gas stream P, thefuel/oxidant mixture is provided at a rate of 3 slm, together with thediluent D at a rate of 8 slm in order to adequately control the flamespeed, temperature and other combustion characteristics within thecombustion chamber in accordance with the reaction (3) to correctlytreat the effluent gas stream P:

10P+CH₄+2O₂+8D(g)=CO₂+8D(I)+2H₂O+10P′  (3)

For example, such a radiant burner 20, operating at approximately 200mbar is fuelled with a hydrocarbon, for example methane, and oxygen.This is diluted to suitable concentration of diluent D.

Since the diluent D condenses in the effluent gas stream P′, it istypically a liquid under ambient conditions and so is heated in order tobe vaporised prior to being provided to the combustion chamber. Theliquid diluent D can therefore be mixed with the fuel and/or with theoxidant in order to store these in a convenient manner prior to beingintroduced into the combustion chamber.

Diluent

In one example, the diluent D is conveniently water. An added advantageof the provision of substantial quantities of water vapour at flametemperature in the combustion chamber is that this provides additionalreagent for F₂ abatement in the effluent gas stream P according toequation (4) below:

F₂+H₂O=2HF+½O₂  (4)

The excess O₂ generated also helps since it reacts with deposition gasessuch as, for example, SiH₄.

The fuel may be dissolved within the water for convenient storage. Forexample, an alcohol may be dissolved within the water to provide anaqueous solution, which is then vaporised prior to being introduced intothe combustion chamber. Likewise, the oxidant may be dissolved withinthe water for convenient storage. For example, hydrogen peroxide may bedissolved within the water to provide an aqueous solution, which is thenvaporised prior to being introduced into the combustion chamber.Similarly, both the fuel and oxidant may be dissolved within the waterfor convenient storage, if this is derived from a 70° C./300 mbarsource, this would require approximately 2600 J/g to produce. The powerto do this would be around:

(8/22.4)×18×2600/60=280 Watts.

This power may be derived from waste heat generated in the vacuum pump.In an integrated system, the water (and the pump) may be pre-heatedelectrically and the temperature maintained by the balance betweenevaporation and heat generation.

Considering the example above where there is around 10 slm of processgas P to be treated, typically, around 1 slm of CH₄ and 2 slm of O₂ willbe required. To dilute this and provide similar combustioncharacteristics as would be achieved with air, around 8 slm of H₂O asthe diluent D will also be needed.

The water condenses within the treated effluent gas stream and so around10 slm of processed effluent gas stream P′, together with 1 slm of CO₂is provided. This means that rather than 19 slm being provided to thesecondary pump stage 30, only around 11 slm is provided, whichconsiderably reduces the amount to be compressed and reduces the powerconsumption to achieve this.

The secondary pump stage 30 may be a liquid ring pump. Providing aliquid ring pump is particularly advantageous as this assists both thecondensation of the diluent and can be used to scrub the gas streamprovided.

Although the above example utilised water as the diluent, it will beappreciated that the diluent may be any suitable compound whichcondenses in the effluent gas stream such as, for example, aperfluorocarbon or a hydrocarbon.

Although illustrative embodiments of the invention have been disclosedin detail herein, with reference to the accompanying drawings, it isunderstood that the invention is not limited to the precise embodimentand that various changes and modifications can be effected therein byone skilled in the art without departing from the scope of the inventionas defined by the appended claims and their equivalents.

1. A process gas abatement apparatus comprising: a burner, and acombustion chamber operable to receive an effluent gas stream from amanufacturing process tool to be treated within the combustion chamberat a sub-atmospheric pressure, the combustion chamber being furtheroperable to receive a fuel, oxidant and diluent, the fuel, oxidant anddiluent controlling combustion within the combustion chamber to treatthe effluent gas stream to produce a treated exhaust stream, the diluentbeing condensable in the treated exhaust stream.
 2. The process gasabatement apparatus of claim 1, wherein the diluent, when introduced tothe combustion chamber, comprises a vapor.
 3. The process gas abatementapparatus of claim 1, wherein the diluent comprises a liquid prior tobeing vaporised for introduction to the combustion chamber.
 4. Theprocess gas abatement apparatus of claim 1, wherein the diluentcondenses to a liquid in the treated exhaust stream.
 5. The process gasabatement apparatus of claim 1 wherein the diluent is introduced intothe combustion chamber with a first volumetric rate and occupies thetreated exhaust stream with a second volumetric rate, the secondvolumetric rate being lower than the first volumetric rate.
 6. Theprocess gas abatement apparatus of claim 1, wherein the diluent iscombined with at least one of the fuel and oxidant prior to beingintroduced into the combustion chamber.
 7. The process gas abatementapparatus of claim 1, wherein at least one of the fuel and the oxidantis dissolved by the diluent prior to being introduced into thecombustion chamber.
 8. The process gas abatement apparatus of claim 1,wherein both the fuel and the oxidant are dissolved by the diluent priorto being introduced into the combustion chamber.
 9. The process gasabatement apparatus of claim 1, wherein at least one of the fuel and theoxidant dissolved by the diluent is vaporised prior to being introducedinto the combustion chamber.
 10. The process gas abatement apparatus ofclaim 1, wherein at least one of the fuel and the oxidant dissolved bythe diluent are co-vaporised prior to being introduced into thecombustion chamber.
 11. The process gas abatement apparatus of claim 1,wherein the diluent comprises at least one of water, a perfluorocarbonand a hydrocarbon.
 12. The process gas abatement apparatus of claim 1,wherein the treated exhaust stream is provided to a liquid ring pump forcompression to atmospheric pressure.
 13. The process gas abatementapparatus of claim 12, wherein the diluent condenses in the liquid ringpump.
 14. The process gas abatement apparatus of claim 12, wherein theliquid ring pump is operable to scrub the treated exhaust stream.
 15. Aprocess gas abatement method, comprising: receiving an effluent gasstream to be treated from a manufacturing process tool within acombustion chamber at a sub-atmospheric pressure; receiving a fuel,oxidant and diluent within the combustion chamber, the fuel, oxidant anddiluent controlling combustion within the combustion chamber to treatthe effluent gas stream to produce a treated exhaust stream; andcondensing the diluent in the treated exhaust stream.